Chronic patellofemoral pain (pain around the knee cap) is one of the most common and potentially debilitating musculoskeletal pain conditions, yet the mechanism of pain development is poorly understood. The most widely accepted theory suggests that pain develops when the patellofemoral joint is subjected to elevated stress (force per unit area). One recently proposed factor contributing to increased patellofemoral joint stress is a movement impairment consisting of medial collapse of the lower extremity during weightbearing. Medial collapse has been described as a combination of excessive adduction and medial rotation of the femur, increased knee valgus, and increased lateral tibial rotation. The kinematic faults that define medial collapse, however, have not been identified in individuals with patellofemoral pain (PFP). Furthermore, it is not clear whether these kinematic faults can be reduced and if so, whether the improved movement pattern leads to a reduction in pain. The broad, long-term objective of the proposed preliminary study is to better understand the relationship between lower extremity movement impairments and symptom behavior in individuals with PFP. Specifically, this study will test whether or not 1) individuals with PFP demonstrate medial collapse during walking, stair climbing and squatting, 2) the kinematic patterns associated with medial collapse are modifiable within a single session, and 3) modified kinematic patterns correspond to changes in pain. Forty subjects will participate (20 PFP, 20 pain-free). Data will be obtained using a 3-dimensional motion analysis system and a visual analog pain scale as subjects perform movement tasks using 1) their preferred pattern, 1) an exaggerated medial collapse pattern, and 3) a corrected medial collapse pattern. Knowledge of the kinematic patterns of individuals with PFP and the relationship between kinematics and symptom behavior will provide insight into the mechanical factors contributing to pain development and help guide future studies aimed at investigating relationships between lower extremity movement impairments, knee joint alignment, and patellar cartilage properties, as well as studies that test intervention and prevention strategies for PFP. PUBLIC HEALTH RELEVANCE: Chronic patellofemoral pain (pain around the knee cap) is a common, potentially debilitating yet poorly understood condition. Knowledge of the specific movement faults that contribute to patellofemoral pain (PFP) and the capacity of individuals to correct the movement faults will inform rehabilitation and prevention strategies for this condition. Ultimately, the number of individuals with PFP, and the disability and cost associated with this condition would be reduced.